A ram boring machine of this kind is disclosed in U.S. Pat. No. 3,995,702. The elastic intermediate piece here acts as damping block and when the machine is in operation absorbs unavoidable shocks and vibrations; these influences should be kept from the reversing gear as far as is possible. Mounting, i.e. installing and disassembling this damping block however requires troublesome manipulation and has considerable disadvantages because the annular damping block is accommodated between a sleeve screwed on to the control pipe and an end piece screwed into the rear end of the machine housing and is secured in its assembled position. Thus, both the damping block and the end piece and the sleeve must be provided with threads, which involves additional manufacturing costs. Aside from this, the screw connection, in particular when unscrewing after the machine has been in operation for a while, causes a lot of difficulties which are particularly due to the adverse influences when making tunnels in the ground which lead to contamination and which are even greater in the case of large machines having diameters reaching up to 450 mm. So that the screw connection does not loosen or become detached due to the vibrations the screw parts are, as a rule, provided with a delicate fine thread and furthermore are often in addition stuck to one another. When disassembling the block this bond has then to be broken by heating at least the threaded sections of the screw parts, so that damage to the damping block caused by heat cannot be avoided.
Other known ram boring machines have a control pipe that is screwed into the rear end of the housing. The control pipe is either in one piece and has an end piece with an external thread which has axial air outlet openings arranged concentrically with the control pipe, or else the end piece is a part separate from the control pipe which is screwed on to the rear end of the control pipe and, together with the control pipe, is screwed into the end of the housing. So that the end piece does not separate from the control pipe or from the housing the threads in these machines are also provided with a metal adhesive before being screwed in. In order to disassemble the end piece the machine housing must likewise be heated in the thread region so as to break the adhesive connection. The screw connection can subsequently be loosened by means of suitable spanners and, if necessary, additional heavy hammer blows, and then unscrewed. This kind of connection between the control pipe and the housing has various disadvantages.
The control pipe has to be secured so that it extends exactly centrally in the axial direction relative to the machine housing and the striking piston so as to avoid leakage between the striking piston and the control pipe and jamming and excessive wear between the control pipe and the striking piston. This can however only be achieved with difficulty with non-centering thread connections. Furthermore the dismantling of the control pipe just described often results in damage to the intermediate piece and the housing. Owing to the rigid connection between the housing, the intermediate piece and the control pipe the vibration and shock caused by the rapid blows of the piston are transmitted undamped to the control pipe and the connection with the compressed air hose. In the case of prolonged use and in difficult operating conditions fatigue fractures can result, in particular in the rear part of the housing of the ram boring machine. The compressed air hose can also become detached from the control pipe so that it must generally be permanently connected to the control pipe by means of a compression sleeve.